Violent dissidence is shaped by specific dynamics. Neither the Red Army Fraction (RAF) nor Al-Qaeda, to name just two prominent examples, started out as terrorist group. Rather, radicalization was a gradual process in both cases. Non-violent forms of dissidence transform into violent forms of dissidence without a distinct threshold. There is often a progression from political resistance to guerrilla warfare to terrorism. This process escalates in two dimensions: there is vertical escalation, in which the means of violence aggravate and rules of conflict are increasingly disregarded, and horizontal escalation, where the group’s geographical range expands. The causes and mechanisms of these types of escalation are unknown. This project studies the mechanisms of escalation of political violence by comparing historical and contemporary cases. Transnational cooperation among non-state actors is a central factor, since it can be assumed to change the opportunity structures of dissident actors so as to enable escalation of violence in the first place. The project aims to explain the role of transnational cooperation in the strategic decisions of dissident actors as well as the transition of radical, but non-violent, resistance into increasingly violent forms of political dissidence – which should also suggest means to reverse this process.